Carrier transmission over power circuits



Nov.'23 1926. 1,607,668

. c. H. FETTER QARRIER TRANSMISSION OVER POWER CIRCUITS Filed April 1924 INVENTOR A TTORNE Y Patented Nov, 1926.

UNITED STATES PATENT OFFICE.

CHARLES rt. rnr'rna, or MILLBURN, EWIJERSE ASSIGNOR 'ro annmcanmmmom: AND TELEGRAPH COMPANY, A CORPORATION on NEW YofiK.

CARRIER TRANSMISSION OVER POWER CIRC' UITS.

Application filed Apri1 29, 1924. Serial No. 709,901.

This invention relatesto the use of power circuits for the transmission of signaling currents, andmore particularly to arrangementswhereby carrier transmission channels 8 may be capacitatively related to the conductors of a power system. r

In accordance with the present ihvention,

a carrier channel-is conductively connected to the conductors of a power circuit in such but being mechanically constructed so as to ower voltages of the withstand the high etween the condensers power conductors.

and the carrier apparatus an inductive shunt is connected across the carrier-conductors to form a lowimpedance path for the low frequency currents employed inv power trans- 3 mission so that, any current of power frequency passingthrough the condenser will be b -passed through the low resistance path.

I the. condensers are designed to offer sufficient impedancejat the power frequencies 'so 'that the =voltage drop at this frequency throu h the by-pass will not be greater than it 'is' esired toi apply to the carrier apparatus, the impedance looking into the condensers at the carrier frequency will be much 85 larger than that looking into the connection to the power conductors, unless the condensers are made so large mechanically that the expense would become prohibitive. 'Owingto this difference in impedance. at the 40 carrier-frequencies, a large reflection loss would occurat the junction of the carrier channel with the power conductors, the impedance looking into the latter being quite -low because of the large amount of copper '45 'employedand because of the numerous parallel branches which are involved in a power system. Accordingl it is proposed by the present invention to cap the condensers of a "reasonable size mechanically .and'to neutralize thereactance of the condensers in part by means of inductances connected in series therewith, the inductances being-s0 proportioned to the condensers that the 1mpedance at the carrier frequency looking into v the condensers will be substantially the same as that looking into the power system.

The invention will now be more fully understood from the detailed description thereof when read in connection with.the accom- .densers 7 and 8 are included in any two of the conductors 1, 2' or 3, said-condensers being illustrated in the conductors 1' and3' 1n order to capacitatively couple the carrier apparatus Tto the power conductors. In order that these condensers may withstand the high voltages impressed uponpower conductors, their plates are made mechanicall quite large and they are widely separate special dielectric materials beingalso. emgloyed in a manner well known in the art. y thus designin the condensers, the amount of current owing through the condensers at .powerfrequencies will be relatively small. A by-pass 12, preferably in ductive and having a very low impedance at power frequencies, will be connected across .the conductors 1 and 3 in order to by-pass the power currents and thereby protect the by-pass element should be designed to have a relatively-high impedance at carrier frequencies.

Fuses 4, 5, and 6 are included in the conductors 1', 2' and 3' in order to protect the carrier apparatus'in case the power current flowing into the carrier channel should build up to a value greater than that for which it is designed. If desired, an additional protector -may be included between the shunt 12and the carrier apparatus. This protector mayv comprise fuses 9 and 10 included in the conductors 1' and .3 and a carbon block. arrangement of well known type having its outerterminals connected 'to the conductors 1 and-3 while the third into the power system from the terminals ofthe carrier channel will be quite low. The impedance looking into the carrier channel, on the other hand, will'be quite high be-' cause of the mechanical limitations on the design of the condensers 7 and 8. The impedance looking into this circuit at the carrier frequenc is, in effect, the series impedance of t e condenser 7, the stepped down impedance of the carrier apparatus, looking through the transformer 16, and the impedance of the condenser 8. The shunt impedance of the by.- ass 12 may be made so high at the carrier requency that the bypass 12 does not materially affect the transfer of energy of carrier frequency between the carrier apparatus andthe power conductors. The impedance, looking into the carrierapparatus T, maybe made as low as desired y means of the step-down transformer 16 so that the principal elements offering an impedance to the flow of the carrier current will be the condensers 7 and 8. Inaccordance with the present invention it is proposed to reduce the effective im-. pedance'of the condensers 7 and 8 at the carrier frequency by including in series therewith neutralizing inductances .17 and.

18. -The inductances 17 and 18 will be designed to neutralize a suflicient amount of the capacity of the condensers 7 and 8 at the carrier fre uency so that the effective impedance loo g into the carrier channel will be substantially equal to the impedance lookingrinto' the power network.

he condensers 7 and 8 and the by-pass 12 prevent the application ofunduly large voltages of the power frequency to the carrier-apparatus. .For example,- let us assume that the power current has afrequency of'60 cycles and thatthe voltage impressed upon the power conductors is 2700 volts.

, at cycles is 5 ohms, the normal power voltage across the terminals of the by-pass 12, and hence across thQftGl'lIliIlfllS of the carrier apparatus, will be about one-half of The condensers 7 and 8 offer such a large imower frequency that the a volt. Suppose, now, one of the condensers, for example, the condenser 8, breaks down so that it is, in effect, short-circuited', the current flowing through the by-pass 12 will begin to build up rapidl until one of the fuses 4, 5 or 6 blows. f the'fuse 6, for example, is designed to blow at 3 amperes, the current flowing through the inductance 12 would not build up to a value greater than 3 amperes, and hence the voltage drop across the terminals of" the by-pass will only be 15 volts, which will not be in excess of that permissible for the carrier apparatus. Should the voltage build up, through the failure of the fuses 4, 5 and 6 to properly function, to too great a value, the current will be by-passed through the carbon block device 11, and one of the fuses 9 or 10 will blow. v

The apparatus associated @with a carrier receiving channel, as illustrated at the right of the diagram, will be in all respects similar to that above described, and no. further reference thereto is necessary. If desired, choke coils 13, 14 and 15 may be included in the power circuit between the carrier terminals and the generator G to prevent transmission of the carrier frequencies to the generator.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely -different;

from those illustrated without departing I from the spirit and scope of the invention as defined in the following claims.

What is claimed is:

1. In a system for signaling over power conductors, a power source, power conductors for transmitting power from .said source 'to a'load, carrier. apparatus, means for couplin said carrier apparatus to said power con uctors comprising condensers so designed mechanically as to withstand high power voltages, and means to partially neutralize the reactance of said condensers at carrier frequencies so that the impedance looking into the carrier channel may be made substantially the same as the impedance looking into the ower network.

2. In a system for signaling over power conductors, a power source, power conductors for transmitting power from said source to a load, carrier apparatus, means for coupling. said carrier apparatus to said power-conductors comprising condensers so designedmechani cally as, to withstand high ower voltages a step-down transformer tween the carrier apparatus and said condensers for stepping down the impedance of thecarrier apparatus to an impedance power network, and means for partially neutralizing the reactance-o'f said condensers at the carrier frequency so that the impedance looking into the said condensers .lower than the impedance looking into the i and the carrier apparatus may be made substantially the same as the impedance looking into the power-network.

3. In a system for signaling over power conductors, a power source, power conductors for transmitting power from said source to a load, carrier apparatus, means for coupling said carrier apparatus to said power conductors comprising condensers so designed mechanically as to withstand high power voltages, a step-down transformer between the carrier apparatus and said condensers for stepping do wn the impedance of the carrier apparatus to an impedance lower than the impedance looking into the power network, means for partially neu tralizing the reactance of said condensers at the carrier frequency so that the impedance looking into said condensers and the carrier apparatus may be made substantially the same as the impedance looking into the power network, and a by-pass bridge across the carrier channel between said condensers and the carrier apparatus, said by-pass offering a very-low impedance to power currents but having a very high impedance at I the carrier frequency 4. In a system for signaling over power conductors, a power source, power conductors for transmitting power from said source to a load, carrier apparatus, means ers at the jcarrier frequency so that the impedance looking into said condensers and a the carrier apparatus may be made-substantially the same as the impedance looking into the power network, a by-pass bridgeacross the carrier channel between said coner currents but having a Very high impedance at the carrier frequency, and fuses included in the carrier conductors, said fuses being designed to open said conductors upon the flow of a power current sufficiently great. to cause a voltage drop through said by-pass greater than that which it is desired shall be applied to the carrier apparatus.

In testimony whereof, 'I'have signed my name to this specification this'26th day of April, 1924. CHARLES H. FETTER.

densers and the carrier apparatus, said bypassv offering a very low impedanceto pow- Y 

